Unlike other 3D display technologies, a spatial light modulator which is a core device reproduces a 3D stereoscopic view of an original object in a holographic display technology. The holographic display technology is characterized in that digital holographic information recording amplitude and phase information of a light wave of the object is loaded into the spatial light modulator, and the light wave of the original object is reproduced using a holographic photoelectric reproduction technology.
The spatial light modulator is a photoelectric device which can be controlled by a signal of a signal source to modulate some parameter of the light wave, e.g., to modulate the amplitude as a result of absorption, to modulate the phase as a function of the refractive index, to modulate the polarization state as a result of rotating a polarization plane, etc., so that the amplitude and phase information of the light wave of the object carried in the signal of the signal source is written into an incident reference light wave. An output light wave thereof is a spatial and temporal function varying with the control signal.
Existing spatial light modulators for holographic displaying generally include a Liquid Crystal Spatial Light Modulator (LC-SLM), a Digital Micro-mirror Device (DMD), and a Photo Reflective Crystal (PRC), where an operating principle of the liquid crystal spatial light modulator is to illuminate a reference light wave onto the liquid crystal spatial light modulator, so that the liquid crystal spatial light modulator is controlled by a signal of a signal source to control liquid crystals to be deflected, using an electric field, to thereby control a light wave to be output, that is, the reference light wave is modulated and then output by the liquid crystal spatial light modulator. The liquid crystal spatial light modulator can be categorized into transmitting and reflecting liquid crystal spatial light modulators dependent upon how the reference light wave is input. FIG. 1A illustrates a schematic diagram of a light path in a transmitting liquid crystal spatial light modulator, where a reference light wave is input to one side of the liquid crystal spatial light modulator 1, and an output light wave modulated by liquid crystals is output from the other side thereof. FIG. 1B illustrates a schematic diagram of a light path in a reflecting liquid crystal spatial light modulator, where a reference light wave is input to and reflected by one side of the liquid crystal spatial light modulator 1, and then an output light wave produced after the reflected light is modulated by liquid crystals is still output from the input side.
FIG. 2A illustrates a structural diagram of a conventional reflecting liquid crystal spatial light modulator, which is a cross sectional view of the structure of the conventional reflecting liquid crystal spatial light modulator, where the structure includes an array substrate 10 and an upper substrate 20, which are arranged opposite to each other, and a liquid crystal layer 30 and photo spacers 40, which are located between the array substrate 10 and the upper substrate 20; a common electrode 21 and a black matrix layer 22 are arranged on the upper substrate 20, and a plurality of pixel electrodes 11, a planarization layer 12 covering the pixel electrodes 11, and reflecting electrodes 13 located on the planarization layer 12 and corresponding respectively to the respective pixel electrodes 11 are arranged on the array substrate 10. In order to increase a storage capacitance, the reflecting electrodes 13 are electrically connected with their corresponding pixel electrodes 11 through through-holes (first through-holes) V running through the planarization layer 12. FIG. 2B illustrates a schematic top view of a part of the conventional reflecting liquid crystal spatial light modulator, where a photo spacer 40 is placed among four adjacent through-holes (first through-holes) V; and since the photo spacer 40 may have such an influence on the distribution of the electric field around it that normal displaying is impossible in the majority of the area proximate to the photo spacer 40, the black matrix layer 22 needs to cover the photo spacer 40, and the area around the photo spacer 40, and the black matrix layer 22 further needs to cover the through-holes (first through-holes) V, thus degrading an aperture opening ratio in the existing spatial light modulator.